Can industrial biological manufacturing
make the case for economies of
unit number?

Contrary to the traditional model of economiesof scale used in industrial chemical manufactur-ing, a model based on economies of unit numberuses facility-level mass production and improve-ments to process design resulting from repeti-tion, a “learning by doing” approach, to reducecapital costs per unit capacity ( 12). Here, “eco-nomies of unit number” can be defined as a shiftfrom a small number of high-capacity units orfacilities to a large number of units or facilitiesoperating at a smaller scale. Through increasingthe number of units produced, this model canleverage cost reduction through mass productionin which costs decline as cumulative outputincreases because of specialization in the pro-duction process and improved process and pro-duct design ( 12). Furthermore, by increasing thenumber of operating units and facilities, cumu-lative experience on the process is gained thatcan uncover a myriad of improvements in design,materials, and production methods ( 12). Thesecontinuous improvements can offer substantialcost reductions as total production volume (i.e.,number of facilities times facility productionrate) increases.

To exploit this economic model in the contextof chemical manufacturing, one can envision thecustom-built, high-CapEx, large-scale operationsbeing replaced with a large number of mass-produced, modular, small-unit-scale technology.This can enable an economies of unit numberapproach that can use automation principles,advances in engineering, and streamlining ofefficient technologies to reduce capital costsper unit capacity. By efficiently scaling down,this type of approach can support small-scale,CapEx- and process-efficient flexible technolo-gies. The smaller-scale and CapEx efficiencyreduces both the time and cost required for com-mercial facilities, enabling rapid, mobile, andwidespread deployment. This model could addressmany of the aforementioned limitations of in-dustrial chemical manufacturing by enabling agreater number of companies to access distributedand sustainable resources and new markets andallowing quick adaptation to both local andglobal market conditions. Although historically,In this context, exploiting the diversity andstrengths of biological processes for fuel and chem-ical production provides the opportunity for CapExand process-efficient technology development,enabling an economies of unit number model.Industrial biomanufacturing employs biologicalcatalysts for the conversion of various feedstocksto fuels and chemicals analogous to those cur-rently produced via chemical manufacturing means(Fig. 2). Biological processes, such as microbialfermentation, efficiently operate at mild temper-atures ( 20° to 100°C) and pressures (atmospheric)and can achieve high carbon- and energy-conversion efficiencies in a single unit operation,which in turn leads to more streamlined and lesstechnologically complex processes ( 13, 14). Indus-trial biocatalysts afford the ability to produce asingle product with an easily adjustable outputat high selectivity without dramatically alteringClomburg et al., Science 2017 355, eaag0804 6 January 2017 2 of 10

Distribution of oil refineries (blue
flame) and corn-ethanol plants (green
leaf) in the United States. Production
capacity is in BOE/day. [Data from
references (90–103); Mapping
and georeferencing copyright
OpenStreetMap and copyright Carto,
respectively] (C) Frequency
distribution of corn-ethanol plants
(green) and oil refineries (blue) in the
United States as a function of their
capacity on an equivalent energy
basis (thousand BOE/day).